Vehicle release state determination device

Abstract

A release state determination device includes: a torque application device configured to apply a control torque to a steering transmission system between a steering wheel and a steered wheel; a steering torque sensor provided in the steering transmission system between the steering wheel and the torque applying device; and a control unit configured so as to determine, when the steering torque detected by the steering torque sensor is within a first predetermined range, a release state in which the driver does not hold the steering wheel, and to control the driver to hold the steering wheel on the basis of the steering torque detected by the steering torque sensor when it is determined that torque is not input to the steering torque sensor. Variable setting of a first predetermined range is performed.

Description

Technical Field

[0001] The present invention relates to a hands-off state determination device for vehicles such as automobiles. Background Art

[0002] As automatic driving devices for vehicles such as automobiles, steering assist devices such as lane keeping assist devices, lane departure prevention devices, and lane change assist devices that control the lateral position of the vehicle relative to the lane by automatic steering are well known.

[0003] The steering assist by the steering assist device is sometimes performed on the premise that the driver is holding the steering wheel (steering handle). It is known that when the driver does not hold the steering wheel, the steering torque (torque) will continue to be small. Therefore, based on the steering torque detected by the steering torque sensor, it is determined whether the driver is not holding the steering wheel and is in a hands-off state.

[0004] For example, Japanese Patent Application Laid-Open No. 2020-117025 describes the following hands-off state determination technology: when the magnitude of the steering torque detected by the steering torque sensor is determined to be less than a reference value for a predetermined number of consecutive times, it is determined that the driver's hands have released the steering wheel. According to this hands-off state determination technology, the driver's hands-off state can be detected without the need for an expensive sensor such as a touch sensor. Summary of the invention

[0005] When the vehicle is in a straight-ahead driving state and neither automatic steering nor steering by the driver is performed, no torque acts on the steering torque sensor, and therefore the steering torque detected by the steering torque sensor is zero.

[0006] However, if there is an error in the assembly (assembly) of the steering device and / or the steering torque sensor, an output error may occur in which the steering torque detected by the steering torque sensor becomes a value other than 0 even if the vehicle is traveling straight and no automatic steering or steering by the driver is being performed. In addition, an output error of the steering torque sensor may occur even if there is a deviation in the wheel alignment of the steering wheels or the left and right weight balance of the vehicle.

[0007] If the output error of the steering torque sensor occurs due to the above factors (main reasons), the magnitude of the steering torque detected by the steering torque sensor will become greater than the reference value due to the output error, and sometimes it is mistakenly judged that the driver is not in the hands-off state even though the driver is in the hands-off state.

[0008] The present invention provides a hands-off state determination device which is improved to reduce the possibility of erroneous determination of whether a driver is in a hands-off state even if an output error of a steering torque sensor is generated due to factors such as assembly error of a steering device.

[0009] According to the present invention, a hands-off state determination device for a vehicle is provided, comprising: a torque application device, configured to apply a control torque to a steering transmission system between a steering wheel and a steering wheel; a steering torque sensor, which is arranged in the steering transmission system between the steering wheel and the torque application device; and a control unit, which is configured to determine that the driver is in a hands-off state without holding the steering wheel when the steering torque detected by the steering torque sensor is within a first predetermined range.

[0010] The control unit is configured to variably set the first predetermined range based on the steering torque detected by the steering torque sensor when it is determined that no torque is input to the steering torque sensor (no torque is input to the steering torque sensor).

[0011] According to the above configuration, the first predetermined range is variably set based on the steering torque detected by the steering torque sensor when it is determined that no torque is input to the steering torque sensor. The steering torque detected by the steering torque sensor when it is determined that no torque is input to the steering torque sensor is an output error of the steering torque sensor caused by factors such as assembly errors of the steering device. Thus, the first predetermined range can be variably set based on the output error of the steering torque sensor. Therefore, compared with the case where the first predetermined range is not variably set, the possibility of the determination of whether the driver is in a hands-off state being erroneously determined due to the output error can be reduced in a case where the output error of the steering torque sensor is generated due to factors such as assembly errors of the steering device.

[0012] In one technical solution of the present invention, the first predetermined range is a range greater than the difference between a base torque and a predetermined value and less than the sum of a base torque and a predetermined value, and the control unit is configured to variably set the first predetermined range by setting the steering torque detected by the steering torque sensor as the base torque when it is determined that no torque is input to the steering torque sensor.

[0013] According to the above technical solution, the first predetermined range is a range that is greater than the difference obtained by subtracting the predetermined value from the reference torque and less than the sum of the reference torque and the predetermined value, and the steering torque detected by the steering torque sensor when it is determined that no torque is input to the steering torque sensor is set as the reference torque. Thus, the first predetermined range can be variably set by variably setting the reference torque based on the steering torque detected by the steering torque sensor when it is determined that no torque is input to the steering torque sensor.

[0014] In another aspect of the present invention, the control unit is configured to determine that no torque is input to the steering torque sensor from the steering wheel side when it is determined that the vehicle is traveling straight and in the center of the lane without a lateral inclination of the road surface.

[0015] When it is determined that the vehicle is traveling straight and in the center of the lane and the road surface is not lateral tilted, no torque acts on the steering torque sensor from the steering wheel side. Therefore, according to the above technical solution, it can be determined that no torque is input to the steering torque sensor from the steering wheel side.

[0016] In another technical solution of the present invention, the control unit is configured to determine that no torque is input from the steering wheel side to the steering torque sensor when it is determined that the vehicle is in a straight-moving state and the magnitude of the lateral force acting on the vehicle is below the lateral force determination reference value and the magnitude of the control torque is below the control torque determination reference value.

[0017] When it is determined that the vehicle is in a straight-moving state and the magnitude of the lateral force acting on the vehicle is less than the lateral force determination reference value and the magnitude of the control torque is less than the control torque determination reference value, no torque acts on the steering torque sensor from the steering wheel side. Therefore, according to the above technical solution, it is possible to determine that no torque is input to the steering torque sensor from the steering wheel side.

[0018] In another technical solution of the present invention, the control unit is configured to determine that no torque is input from the steering wheel side to the steering torque sensor when the steering torque detected by the steering torque sensor is within a second predetermined range greater than a first predetermined range under the condition that no torque is input from the steering wheel side to the steering torque sensor.

[0019] In a situation where no torque is input from the steering wheel side to the steering torque sensor, when the driver does not perform a steering operation but gently holds the steering wheel, the magnitude of the steering torque detected by the steering torque sensor does not become a large value. According to the above technical solution, when the steering torque detected by the steering torque sensor is within a second predetermined range greater than the first predetermined range, it is determined that no torque is input from the steering wheel side to the steering torque sensor. Thus, it is possible to determine a situation where the driver does not perform a steering operation but gently holds the steering wheel and no torque is input from the steering wheel side to the steering torque sensor.

[0020] Other objects, other features and attendant advantages of the present invention will be easily understood from the following description of the embodiments of the present invention with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described below with reference to the accompanying drawings, in which like reference numerals represent like elements, and in which:

[0022] Figure 1 is a schematic diagram showing the structure of a hands-free state determination device according to an embodiment;

[0023] Figure 2 is a flowchart showing a hands-off state determination control routine of the first embodiment;

[0024] Figure 3 is a flowchart showing a hands-off state determination control routine according to the second embodiment;

[0025] Figure 4 is a flowchart showing a hands-off state determination control routine according to the third embodiment;

[0026] Figure 5 is a flowchart showing a hands-off state determination control routine according to a fourth embodiment;

[0027] Fig. 6A 1 is a diagram showing an example of hands-off state determination in a case where the reference value Tr is not variably set in the prior art;

[0028] Figure 6B 1 is a diagram showing an example of hands-off state determination when the reference value Tr is variably set according to the present invention. DETAILED DESCRIPTION

[0029] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0030] like Figure 1 As shown, the hands-off state determination device 100 according to the embodiment is applied to an automatically driven vehicle 102, which includes a steering device 10, an electric power steering ECU 40, and a steering assist ECU 50, and is provided with a drive ECU 60 and a brake ECU 70. In this specification, the electric power steering is referred to as EPS (Electric Power Steering) as needed.

[0031] EPS-ECU 40, steering assist ECU 50, drive ECU 60 and brake ECU 70 are electronic control devices with microcomputers as main parts, which are connected via CAN (Controller Area Network) 104 in a manner that can send and receive information to each other. Each microcomputer includes a CPU, ROM, RAM, non-volatile memory and interface, etc. The CPU implements various functions by executing instructions (programs, routines) stored in the ROM. These ECUs can also be integrated into one ECU.

[0032] like Figure 1 As shown, the steering device 10 includes an EPS device 12 connected to the EPS-ECU 40, and the EPS device 12 is configured as a rack and pinion type EPS device that is driven in response to the driver's operation of the steering wheel 14. The rack bar 18 of the EPS device 12 is connected to the knuckle arms (not shown) of the front wheels 16FL and 16FR as steering wheels via tie rods 20L and 20R. The steering wheel 14 is connected to the pinion shaft 26 of the EPS device 12 via the steering shaft 22 and the universal joint 24.

[0033] In the illustrated embodiment, the EPS device 12 is a rack-assisted electric power steering device having an electric motor 28 and a conversion mechanism 30, such as a belt-type conversion mechanism 30, which converts the rotation and torque of the electric motor 28 into displacement and force in the reciprocating direction and transmits them to the rack bar 18. The EPS device 12 generates a control torque by driving the rack bar 18 relative to the housing 32.

[0034] Thus, the steering shaft 22, the universal joint 24, the pinion shaft 26, the EPS device 12, and the tie rods 20L and 20R constitute a steering transmission system 34 that transmits steering displacement and torque between the steering wheel 14 and the front wheels 16FL and 16FR. The EPS device 12 cooperates with the EPS-ECU 40 and functions as a torque applying device that applies a control torque Tc to the steering transmission system 34.

[0035] The steering shaft 22 is provided with a steering angle sensor 36 that detects a steering angle θs, and the pinion shaft 26 is provided with a steering torque sensor 38 that detects a steering torque Ts. Figure 1 Although not shown in detail, the steering torque sensor 38 detects the difference in rotation angle between the components on the steering wheel 14 side and the components on the EPS device 12 side relative to the torsion bar that can be elastically twisted and deformed, that is, a value proportional to the relative rotation angle, as the steering torque Ts. The steering torque sensor 38 can also be provided on the steering shaft 22.

[0036] In addition, the steering angle θs and the steering torque Ts are set to be positive values ​​when the vehicle 102 turns left according to the driver's steering operation. As long as the control torque is applied to the steering transmission system 34 between the front wheels 16FL and 16FR and the steering torque sensor 38, the EPS device 12 can also be a pinion-assisted type or a steering column-assisted type EPS device.

[0037] The EPS-ECU 40 controls the steering assist torque and reduces the driver's steering burden by controlling the EPS device 12 based on the steering torque Ts and the vehicle speed V detected by the driving operation sensor 80 and the vehicle state sensor 90 described later in a manner known in the technical field. In addition, the EPS-ECU 40 can steer the front wheels 16FL and 16FR as needed by controlling the EPS device 12. Thus, the EPS-ECU 40 and the EPS device 12 function as an automatic steering device that automatically steers the front wheels as needed.

[0038] The steering assist ECU 50 is connected to a camera sensor 52 and a radar sensor 54. The camera sensor 52 and the radar sensor 54 include a plurality of camera devices and a plurality of radar devices, respectively. The camera sensor 52 and the radar sensor 54 function as a target information acquisition device that acquires information of at least a target in front of the vehicle 102. In addition, a LiDAR (Light Detection And Ranging) may be used instead of the radar sensor 54 or in addition to the radar sensor 54.

[0039] Furthermore, the steering assist ECU 50 is also connected to a setting operator 56 and an alarm device 58. The setting operator 56 is provided at a position operated by the driver. Figure 1 Although not shown in the figure, in the embodiment, the operator 56 is set to include an LTA switch, and the steering assist ECU 50 executes LTA when the LTA switch is turned on. In addition, the LTA switch may be omitted. In addition, LTA means Lane Tracing Assist Control.

[0040] The alarm device 58 is activated when it is determined that the driver is not in the hands-off state of the steering wheel 14, and an alarm is sounded, that is, an alarm indicating that the driver is in the hands-off state. The alarm device 58 may be any one of the following alarm devices, or any combination thereof: an alarm device that sounds a visual alarm such as a display or an alarm light; an alarm device that sounds an audible alarm such as an alarm buzzer; and an alarm device that sounds a physical alarm such as a seat vibrating alarm.

[0041] The driving ECU 60 is connected to a driving device 62. Figure 1 The driving wheel (not shown) applies driving force to accelerate the vehicle 102. Normally, the driving ECU 60 controls the driving device 62 in such a way that the driving force generated by the driving device 62 varies according to the driving operation performed by the driver. When receiving a command signal from the steering assist ECU 50, the driving ECU 60 controls the driving device 62 based on the command signal.

[0042] The brake ECU 70 is connected to a brake device 72. Figure 1 The vehicle 102 is decelerated by applying braking force to the wheels not shown in the figure. Normally, the brake ECU 70 controls the brake device 72 in such a way that the braking force generated by the brake device 72 varies according to the brake operation performed by the driver. When receiving a command signal from the steering assist ECU 50, the brake ECU 70 controls the brake device 72 based on the command signal, thereby performing automatic braking.

[0043] The driving operation sensor 80 and the vehicle state sensor 90 are connected to the CAN 104. Information detected by the driving operation sensor 80 and the vehicle state sensor 90 (referred to as sensor information) is sent to the CAN 104. The driving operation sensor 80 includes a driving operation amount sensor and a braking operation amount sensor. The vehicle state sensor 90 includes a vehicle speed sensor, a front and rear acceleration sensor, a lateral acceleration sensor, and a yaw rate sensor.

[0044] The steering assist ECU50 is a central control device for performing steering assist control. In the embodiment, the steering assist ECU50 executes LTA in cooperation with other ECUs. Steering assist controls such as LTA are performed on the premise that the driver is holding the steering wheel 14. Therefore, in the first to fourth embodiments described below, the steering assist ECU50 performs a hands-off state determination control for determining whether the driver is not holding the steering wheel 14 but has let go of his hands. When the steering assist ECU50 determines that the hands-off state is present during the execution of LTA, the alarm device 58 is operated to sound an alarm, and the control amount of LTA is gradually reduced to end LTA. In addition, the control of LTA is well known in the technical field and does not constitute the main purpose of the present invention, so its description is omitted.

[0045] First embodiment

[0046] In the first embodiment, the ROM of the steering assist ECU 50 stores Figure 2 The flowchart shown in FIG. 1 corresponds to the hands-off state determination control procedure. Figure 1 When the LTA switch (not shown) is turned on and LTA is being executed, according to Figure 2The hands-off state determination control in the flowchart shown is repeatedly executed by the CPU of the steering assist ECU 50 at predetermined intervals. This is also the same for the hands-off state determination control in other embodiments described later. In addition, when the hands-off state determination control starts, the reliability R described later is initialized to 0.

[0047] In S10, the CPU determines whether the vehicle 102 is in a straight-ahead driving state. When the CPU makes a negative determination, the control enters S90, and when the CPU makes an affirmative determination, the control enters S20. In this case, the curvature of the lane can be estimated based on the image in front of the vehicle 102 captured by the camera sensor 52, and the inclination angle of the traveling direction of the vehicle 102 relative to the lane can be estimated. Furthermore, for example, when the absolute value of the curvature of the lane is less than the reference value (positive constant) for curvature determination and the absolute value of the inclination angle of the traveling direction is less than the reference value (positive constant) for inclination angle determination, it can be determined that the vehicle 102 is in a straight-ahead driving state. In addition, the determination of the inclination angle of the traveling direction can also be omitted.

[0048] In S20, the CPU determines whether the vehicle 102 is traveling in the center of the lane. When the CPU makes a negative determination, the control proceeds to S90, and when the CPU makes an affirmative determination, the control proceeds to S30. In this case, for example, the magnitude of the offset (deviation) of the lateral position of the center of the vehicle width direction relative to the center of the lane width direction can be estimated. Furthermore, when the magnitude of the offset of the lateral position is less than the reference value (positive constant) for the offset determination for more than the first reference time (positive constant), it can be determined that the vehicle 102 is traveling in the center of the lane.

[0049] In S30, the CPU determines whether the road surface has no lateral inclination. When the CPU makes a negative determination, that is, when it determines that the road surface has a lateral inclination, the present control proceeds to S90, and when it makes an affirmative determination, the present control proceeds to S40. In this case, when the absolute value of the lateral acceleration Gy of the vehicle 102 detected by the lateral acceleration sensor of the vehicle state sensor 90 is less than the reference value (positive constant) of the lateral acceleration and the absolute value of the yaw rate Yr of the vehicle 102 detected by the yaw rate sensor is less than the reference value (positive constant) of the yaw rate, it can be determined that the road surface has no lateral inclination.

[0050] In S40, the CPU determines whether the driver is holding the steering wheel 14 lightly without performing a steering operation. When the CPU makes a negative determination, the control proceeds to S90, and when the CPU makes an affirmative determination, the control proceeds to S50. In this case, when the steering torque Ts detected by the steering torque sensor 38 falls within a second predetermined range of a lower limit value Trf-β or more and an upper limit value Trf+β or less for a second reference time (positive constant) or more, it can be determined that the driver is holding the steering wheel 14 lightly. In addition, β can be a positive constant greater than α in S100 described later, and Trf is the previous value of the reference value Tr for hands-off state determination set in S80 or S90 described later.

[0051] In S50, the CPU calculates the average value Ta of the steering torque Ts detected by the steering torque sensor 38. In this case, the steering torque Ts used to calculate the average value Ta may be limited to a value from the present to a predetermined time ago or a value of a predetermined number of control cycles.

[0052] In S60 , the CPU calculates the reliability R by adding 1 to the previous value of the reliability R. Note that the reliability R may be reset to 0 when the vehicle 102 ends its travel.

[0053] In S70, the CPU determines whether the reliability R is greater than or equal to a reference value R0 (a positive constant integer). When the CPU makes an affirmative determination, in S80, the reference value Tr for hands-off state determination is set to the average value Ta calculated in S50. In contrast, when the CPU makes a negative determination, the reference value Tr for hands-off state determination is set to a preset reference value Tr0 (e.g., 0).

[0054] In S100, the CPU sets α to a positive constant and determines whether the steering torque Ts detected by the steering torque sensor 38 is within a first predetermined range of a lower limit value Tr-α or more and an upper limit value Tr+α or less. When the CPU makes a positive determination, it determines in S110 that the driver is in a hands-off state, and activates the alarm device 58 to issue an alarm indicating that the driver is in a hands-off state. In contrast, when the CPU makes a negative determination, it does not determine in S120 that the driver is in a hands-off state, and when an alarm is being issued, it stops the alarm and temporarily terminates the control. In addition, when no alarm is issued, the CPU temporarily terminates the control.

[0055] According to the first embodiment, when the vehicle 102 is traveling straight and the vehicle is traveling in the center of the lane and the road surface is not tilted laterally, an affirmative determination is made in S10 to S30. Thus, according to S10 to S30, it can be determined that no torque is input from the front wheels 16FL, 16FR, which are steering wheels, to the steering torque sensor 38. In addition, when the torque Ts detected by the steering torque sensor is within a second predetermined range greater than the first predetermined range for a second reference time or longer, an affirmative determination is made in S40. Thus, according to S40, it can be determined that no torque is input from the steering wheel 14 to the steering torque sensor.

[0056] Second embodiment

[0057] In the second embodiment, the ROM of the steering assist ECU 50 stores Figure 3 The flowchart shown in FIG. 1 corresponds to the hands-off state determination control procedure. Figure 1 When the LTA switch (not shown) is turned on and LTA is being executed, according to Figure 3 The hands-off state determination control in the flowchart shown is repeatedly executed by the CPU of the steering assist ECU 50 at predetermined time intervals.

[0058] according to Figure 3 and Figure 2 As can be seen from the comparison, S10 and S40 to S120 are executed in the same manner as in the first embodiment, and when an affirmative determination is made in S10, S25 is executed.

[0059] In S25, the CPU determines whether the magnitude of the lateral force acting on the vehicle 102 is less than the reference value of the lateral force. When the CPU makes a negative determination, the control proceeds to S90, and when the CPU makes an affirmative determination, the control proceeds to S35. In this case, when the absolute value of the lateral acceleration Gy of the vehicle 102 detected by the lateral acceleration sensor of the vehicle state sensor 90 is less than the reference value (positive constant) of the lateral acceleration and the absolute value of the yaw rate Yr of the vehicle 102 detected by the yaw rate sensor is less than the reference value (positive constant) of the yaw rate, it can be determined that the magnitude of the lateral force acting on the vehicle is less than the reference value of the lateral force.

[0060] The lateral acceleration Gy of the vehicle 102 may be replaced by an estimated lateral acceleration calculated based on the steering angle θs detected by the steering angle sensor 36 and the vehicle speed detected by the vehicle speed sensor. In addition, the determination of the yaw rate may be omitted.

[0061] In S35, the CPU determines whether the absolute value of the control torque Tc applied by the EPS device 12 to the steering transmission system 34 is less than the reference value Tc0 (positive constant) of the control torque. If the CPU makes a negative determination, the control proceeds to S90, and if the CPU makes an affirmative determination, the control proceeds to S40.

[0062] According to the second embodiment, when it is determined that the vehicle 102 is traveling straight and the lateral force acting on the vehicle is less than the reference value and the magnitude of the control torque Tc is less than the reference value, an affirmative determination is made in S10, S25 and S35. Thus, according to S10, S25 and S35, it can be determined that no torque is input from the front wheels 16FL and 16FR, which are steering wheels, to the steering torque sensor 38. In addition, as in the first embodiment, when the torque Ts detected by the steering torque sensor continues to be within a second predetermined range greater than the first predetermined range for more than the second reference time, an affirmative determination is made in S40. Thus, it can be determined that no torque is input from the steering wheel 14 to the steering torque sensor.

[0063] Third embodiment

[0064] In the third embodiment, the ROM of the steering assist ECU 50 stores Figure 4 The flowchart shown in FIG. 1 corresponds to the reference value Tr calculation control procedure. Figure 1 When the LTA switch (not shown) is turned on and LTA is being executed, according to Figure 4 The reference value Tr calculation control in the flowchart shown is repeatedly executed by the CPU of the steering assist ECU 50 at predetermined time intervals.

[0065] according to Figure 4 and Figure 2 As can be seen from the comparison, S10 to S80 are performed in the same manner as in the first embodiment, and when S80 is completed, the present control returns to S10. Figure 4 Although not shown, S100 to S120 of the first and second embodiments are executed as a hands-off state determination routine separate from the routines of S10 to S80. This is also the case in the fourth embodiment described later.

[0066] In the third embodiment, the average value Ta of the steering torque Ts calculated in S50 is stored in the nonvolatile memory when the vehicle 102 ends its travel. Furthermore, when the present control starts, before S10, in S5, the reference value Tr used for the determination in S100 is set to the average value Ta stored in the nonvolatile memory.

[0067] Fourth embodiment

[0068] In the fourth embodiment, the ROM of the steering assist ECU 50 stores Figure 5 The flowchart shown in FIG. 1 corresponds to the reference value Tr calculation control procedure. Figure 1 When the LTA switch (not shown) is turned on and LTA is being executed, according to Figure 5 The reference value Tr calculation control in the flowchart shown is repeatedly executed by the CPU of the steering assist ECU 50 at predetermined time intervals.

[0069] according to Figure 5 and Figure 2 As can be seen from the comparison, S10, S25, S35, and S40 to S80 are executed in the same manner as in the third embodiment, and when an affirmative determination is made in S10, S25 is executed.

[0070] In the fourth embodiment, similarly to the third embodiment, the average value Ta of the steering torque Ts calculated in S50 is stored in the nonvolatile memory when the vehicle 102 ends its travel. Furthermore, when the present control starts, before S10, in S5, the reference value Tr used for the determination in S100 is set to the average value Ta stored in the nonvolatile memory.

[0071] As can be seen from the above description, according to each embodiment, when it is determined that no torque is input to the steering torque sensor 38, the average value Ta of the steering torque Ts detected by the steering torque sensor in this state is calculated, and the reference value Tr is set to the average value Ta. Furthermore, based on the average value Ta, the first predetermined range for determining the hands-off state is variably set to be a range greater than or equal to the lower limit value Tr-α and less than or equal to the upper limit value Tr+α.

[0072] The steering torque Ts detected by the steering torque sensor 38 when it is determined that no torque is inputted thereto is an output error of the steering torque sensor due to factors such as assembly error of the steering device.

[0073] Thus, according to each embodiment, the first predetermined range can be variably set based on the output error of the steering torque sensor. Therefore, compared with the case where the first predetermined range is not variably set, the possibility of erroneous determination of whether the driver is in the hands-off state can be reduced in the case where the output error of the steering torque sensor occurs due to factors such as assembly error of the steering device.

[0074] For example, Fig. 6A An example of hands-off state determination is described with respect to the conventional case where the reference value Tr is not variably set. Figure 6B An example of hands-off state determination is shown for the case where the reference value Tr is variably set according to the present invention. Fig. 6A , Figure 6BIn FIG. 1 , the dotted line indicates the average value Ta of the steering torque Ts detected by the steering torque sensor, and the average value Ta is ΔTs (ΔTs is a negative value). As in the conventional hands-off state determination device, the reference value Tr is set to 0 in the conventional case where the reference value Tr is not variably set.

[0075] In the past, when the reference value Tr was not variably set, even if the driver was in the hands-off state, the steering torque Ts was judged to exceed the first predetermined range in the area where the steering torque Ts was smaller than the lower limit value -α of the predetermined range (the hatched area), and it was mistakenly judged that the driver was holding the steering wheel 14.

[0076] In contrast, according to each embodiment, the reference value Tr is set to the average value Ta, and the first predetermined range for determining the hands-off state is set to a range greater than the lower limit value Tr-α and less than the upper limit value Tr+α. Thus, even in the hatched area in the conventional case where the reference value Tr is not variably set, it can be determined that the steering torque Ts does not exceed the predetermined range, and that the driver is in the hands-off state.

[0077] In particular, according to each embodiment, the reliability R is calculated so that the greater the number of times that the torque is determined not to be input to the steering torque sensor 38, the higher the reliability R is, and when the reliability R is equal to or greater than the reference value R0, the reference value Tr is set to the average value Ta. Thus, compared with the case where the reference value Tr is set to the average value Ta regardless of the number of times that the torque is determined not to be input to the steering torque sensor 38, the reference value Tr can be made closer to the value of the steering torque Ts that the steering torque sensor 38 should originally output. Therefore, compared with the case where the reference value Tr is set to the average value Ta regardless of the reliability R, whether the driver is in the hands-off state can be accurately determined.

[0078] As mentioned above, although the specific embodiment and modification of the present invention are described in detail, the present invention is not limited to the above-mentioned embodiment and modification, it is obvious to those skilled in the art that various other embodiments can be implemented within the scope of the present invention.

[0079] For example, in each of the above-described embodiments, the steering assist control is LTA, but it may be any steering assist control that controls the lateral position of the vehicle relative to the lane by automatic steering, such as lane departure prevention control or lane change assist control.

[0080] In the embodiment, LTA is performed on the premise that the driver is not in a hands-off state, in other words, holding the steering wheel. However, steering assist control such as LTA may be performed regardless of whether the driver is in a hands-off state, and when the end condition of the steering assist control is met, it is determined whether the driver is in a hands-off state.

[0081] In addition, the first to fourth embodiments described above are performed independently of each other. However, at least one of S20 and S30 of the first embodiment may be incorporated into the second embodiment. Conversely, at least one of S25 and S35 of the second embodiment may be incorporated into the first embodiment.

[0082] Likewise, at least one of S20 and S30 of the third embodiment may be incorporated into the fourth embodiment. Conversely, at least one of S25 and S35 of the fourth embodiment may be incorporated into the third embodiment.

[0083] Furthermore, in the first and third embodiments, when a negative determination is made in any one of S10 to S40, the reliability R may be reduced or reset to 0. Similarly, in the second and fourth embodiments, when a negative determination is made in any one of S10, S25, S35, and S40, the reliability R may be reduced or reset to 0.

Claims

1. A hands-free state determination device for a vehicle, comprising: a torque applying device configured to apply a control torque to a steering transmission system between a steering wheel and a steering wheel; a steering torque sensor disposed in the steering transmission system between the steering wheel and the torque applying device; as well as a control unit configured to determine that the driver is in a hands-off state without holding the steering wheel when the steering torque detected by the steering torque sensor is within a first predetermined range, The control unit is configured to variably set the first predetermined range based on the steering torque detected by the steering torque sensor when it is determined that no torque is input to the steering torque sensor.

2. The vehicle hands-free state determination device according to claim 1, The first predetermined range is a range that is greater than a difference between a base torque and a predetermined value and less than a sum of the base torque and the predetermined value. The control unit is configured to variably set the first predetermined range by using, as the reference torque, a steering torque detected by the steering torque sensor when it is determined that no torque is input to the steering torque sensor.

3. The vehicle hands-free state determination device according to claim 1, The control unit is configured to determine that no torque is input to the steering torque sensor from the steering wheel side when it is determined that the vehicle is traveling straight and the vehicle is traveling in the center of a lane and the road surface is not lateral tilted.

4. The vehicle hands-free state determination device according to claim 1, The control unit is configured to determine that no torque is input to the steering torque sensor from the steering wheel side when it is determined that the vehicle is in a straight-moving state and the magnitude of the lateral force acting on the vehicle is less than a lateral force determination reference value and the magnitude of the control torque is less than a control torque determination reference value.

5. The vehicle hands-free state determination device according to claim 1, The control unit is configured to determine that no torque is input from the steering wheel side to the steering torque sensor when the steering torque detected by the steering torque sensor is within a second predetermined range larger than the first predetermined range under a condition where no torque is input from the steering wheel side to the steering torque sensor.

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